We're dividing 618525 by 21 
The aim is to understand the frequency of 21 in 618525.

Step 1:
21 goes into 6 0 times with a remainder of 6.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtract 0 from 6 to get 6.
Grab the next digit (1) from the dividend, add it to 6, then carry on: 61 / 21

Advancing to step 2:
21 goes into 61 2 times with a remainder of 19.
Use 2 as the next digit of our solution. 
Result so far: 2.0
If we take 42 away from 61, we end up with 19.
Include the next digit (8) from the dividend after 19, then repeat: 198 / 21

Advancing to step 3:
21 goes into 198 9 times with a remainder of 9.
The next digit of our result is 9. 
Result so far: 29.0
Subtracting 189 from 198 leaves us with 9.
Take the next digit (5) from the dividend and append it to 9, then repeat: 95 / 21

Step 4:
95 divided by 21 is 4 with a remainder of 11.
Write down 4 as next digit of the result. 
Result so far: 294.0
If we take 84 away from 95, we end up with 11.
Grab the next digit (2) from the dividend, add it to 11, then carry on: 112 / 21

Going ahead to step 5:
When dividing 112 by 21, we get 5 with a remainder of 7.
Use 5 as the next digit of our solution. 
Result so far: 2945.0
If we subtract 105 from 112, we get 7.
Fetch the next digit (5) from the dividend, attach it to 7 and continue: 75 / 21

Step 6:
75 divided by 21 is 3 with a remainder of 12.
The next digit of our result is 3. 
Result so far: 29453.0
Deduct 63 from 75 and we're left with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Step 7:
120 divided by 21 is 5 with a remainder of 15.
Use 5 as the next digit of our solution. 
Result so far: 29453.5
If we take 105 away from 120, we end up with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

On to step 8:
21 can be fit into 150 7 times, resulting in a remainder of 3.
The number 7 becomes the next digit in our result. 
Result so far: 29453.57
The remainder is 3 after subtracting 147 from 150.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

On to step 9:
21 goes into 30 1 times with a remainder of 9.
Use 1 as the next digit of our solution. 
Result so far: 29453.571
Deduct 21 from 30 and we're left with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Step 10:
21 can be fit into 90 4 times, resulting in a remainder of 6.
Record the quotient 4 as the next digit in the result. 
Result so far: 29453.5714
Deduct 84 from 90 and we're left with 6.
Since there are no more digits in the dividend, we add a zero to the remainder making it 60, and continue the process.

Moving on to step 11:
When dividing 60 by 21, we get 2 with a remainder of 18.
The next digit of our result is 2. 
Result so far: 29453.57142
Subtracting 42 from 60 leaves us with 18.
Since there are no more digits in the dividend, we add a zero to the remainder making it 180, and continue the process.

On to step 12:
180 divided by 21 is 8 with a remainder of 12.
Use 8 as the next digit of our solution. 
Result so far: 29453.571428
The remainder is 12 after subtracting 168 from 180.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Advancing to step 13:
The number 21 fits into 120 5 times, leaving a remainder of 15.
The number 5 becomes the next digit in our result. 
Result so far: 29453.5714285
Deduct 105 from 120 and we're left with 15.
Since there are no more digits in the dividend, we add a zero to the remainder making it 150, and continue the process.

Step 14:
21 can be fit into 150 7 times, resulting in a remainder of 3.
The number 7 becomes the next digit in our result. 
Result so far: 29453.57142857
Deduct 147 from 150 and we're left with 3.
Since there are no more digits in the dividend, we add a zero to the remainder making it 30, and continue the process.

Our division results in 29453.57142857 with a remaining 3e-09.